1. Field of the Invention
The present invention relates to workpiece engaging tools used in manufacturing operations and, specifically, to gripping, clamping, piercing and hemming devices for engaging and/or performing work on workpieces.
2. State of the Art
In manufacturing operations, various types of tools are employed to engage workpieces and/or to perform work on such workpieces. Typically, grippers and clamps are used to engage workpieces at the completion of one manufacturing operation and to remove such workpieces from one work station for subsequent transport to another work station or to a storage location.
In a typical stamping operation in which metal sheets are progressively formed to a final shape through a series of work operations in adjacently disposed stamping presses, grippers are employed to remove the metal sheet from each press and, in combination with additional parts handling equipment, to deposit the workpiece in an adjacent press or an intermediate idle station located between adjacent presses.
Typically, such grippers are formed of a number of interconnected pins and links which effect opening and closing of gripper jaws. Such mechanisms are complicated in construction and high in cost. Further, the pins and links of such grippers are employed to drive the gripper jaws into a position engaging the workpiece. This provides an inefficient and variable force to grip such workpieces.
In hemming applications, such as the manufacture of vehicle doors, deck lids, etc., the edge of one sheet of metal is bent around the edge of an upper disposed sheet to join the two sheets of metal together Typically, a complex and elaborate machine is employed to bend the edge of the lower sheet about the upper sheet. Such machines utilize a complex arrangement of fluid cylinders and links to effect the bending of the metal sheet edge.
In piercing operations, a punch is brought under high force into engagement with a workpiece, typically in the form of one or more metal sheets. The workpiece or metal sheets are supported on a die which has a through bore extending therethrough. The punch is forced through the workpiece or sheet metal into the bore in the die to form an aperture in the workpiece.
In a previous pierce apparatus devised by the Applicant, a pierce unit was constructed utilizing two pairs of opposed upper and lower arms pivotally mounted to a housing. A drive pin mounted on the end of an extensible, fluid operated, cylinder piston rod extended through a pair of central guide plates having linear cams formed therein to guide the drive pin in a linear path. The drive pin also engaged cams formed in each of the upper and lower arms, FIG. 10, to pivot the arms between a spaced-apart open position and a closed, workpiece engaging position. A punch or pierce unit was mounted on the upper arms and a die was mounted on the lower arms.
The cams in each of the upper and lower arms had a generally open L-shape with the two substantially linear portions of each cam being disposed at an interior obtuse angle with respect to each other. While this cam shape effectively moved the arms between open and closed positions during movement of the drive pin therealong and generated sufficient force to drive the punch through the workpiece, a problem occurred when the arms were moved to the full open position by retraction of the piston rod and drive pin attached thereto. When the drive pin reached the extreme end, the leftmost end in FIG. 1, the drive pin was directly in line with the pivot pin connecting the pivotal arms to the surrounding guide housing. The cam through which the drive pin was to be urged during subsequent extension of the drive pin and cylinder piston rod was thus disposed at a substantially 90.degree. angle with respect to a line extending between the drive pin and the pivot pin. This resulted in frequent locking of the pivotal arms in the open position and, even if the drive pin was able to be driven from the end of the cam, a non-smooth operation of the pierce unit resulted.
Thus, it would be desirable to provide a workpiece engaging apparatus for manufacturing operations which has a high workpiece engaging force and, yet, is simple in design. It would also be desirable to provide a workpiece engaging apparatus for manufacturing operations which overcomes the problems encountered with previously devised pierce apparatus. It would also be desirable to provide a workpiece engaging apparatus particularly suited for piercing applications which has a smooth, non-locking operation.